Om Namah Shivaya (Panchakshara Mantra or Mantra of the five syllables) is one of the most powerful and well-known mantras in the Hindu tradition, being the basis of the teachings of the Vedas and Tantrums.
Its intonation is often used in Himalayan traditions as well as in related traditions, especially Hinduism. It is said that its continuous recitation (jap) and meditation on the meaning of this mantra leads to self-realization.
OM/AUM: The three sounds that form the first syllable of OM (A-U-M) describe the three states of consciousness: the waking state, the dream state and the state of deep sleep without dreams, the three levels of manifestation: the coarse level, the subtle level and the causal level, and the three levels of the mind: conscious, unconscious and subconscious just like the three universal processes of existence, birth, existence and death.
The absolute silence between the three levels is the silence that follows the AUM, and it also refers to Tripura, or to the one who lives in the "three cities" similar to other mantras, for example the Gayatri Mantra.
Namah/ Namaha: it means adoration, respect, homage. Nothing is truly mine (as an individual person) it all belongs to the Absolute Reality. The three levels of the sacred syllable OM, the coarse, subtle and causal state, described above, do not belong to us as real properties of the one who really exists.
It is truly not "nothing of mine", rather everything that is part of this triad belongs to the "other" or to the Absolute Reality.
Shivaya/Shiva: The Absolute Reality is the one that represents the potential from which everything that exists is born. When we realize that nothing is truly separate, we come to see that we are all part of this Absolute Reality. Shiva – the supreme consciousness, and Shakti its creative, active aspect, are seen as one and the same thing. When the union between Shiva and Shakti is realized, through direct experience, it reflects the union of the three worlds (levels) or Tripura that are contained by the sacred syllable AUM.